1. Field of the Invention
The present invention relates generally to an uplink scheduling method in a wireless communication system, and in particular, to a method of scheduling uplink resources for Extended Real-Time Polling Service (ertPS) supporting Voice over Internet Protocol (VoIP).
2. Description of the Related Art
A scheduling scheme is needed to efficiently use resources in a wireless communication system which provides a variety of services with limited resources. It is ideal that unnecessarily allocated resources are rapidly returned and re-allocated to necessary services. Also, it is necessary to reduce the amount of information sent with wireless resources and use the extra resources for other purposes.
Many uplink scheduling schemes have been proposed for VoIP. They include Unsolicited Grant Service (UGS), Real-Time Polling Service (rtPS), and ertPS.
In UGS, a fixed amount of uplink resources are allocated upon user request. Hence, a user transmits data with the allocated uplink resources. rtPS allocates required resources in response to a periodic uplink resource allocation request from the user. The user transmits data with resources appropriately allocated according to the amount of the data.
FIG. 1 illustrates a conventional uplink resource scheduling for UGS.
Referring to FIG. 1, the status of a Mobile Station (MS) is divided into a talk-spurt period and a silence period on the time axis. The talk-spurt period is an on-period with transmission of data packets from the MS, while the silence period is an off-period without any transmission of data packet. The same resources are allocated to the MS during both periods. In the illustrated case of FIG. 1, resources supporting a full rate, Rate 1 are constantly allocated.
However, the MS does not use all the allocated resources in transmitting data. During silence periods 110 and 118, the MS uses only minimum resources required to maintain the service (e.g. Rate ⅛).
It occurs that only a fraction of the allocated resources are used during the talk-spurt period. In other words, the MS transmits data packets using the whole or part of the resources during the talk-spurt period. For instance, the MS transmits data packets at Rate 1, that is, using the entire allocated resources during a talk-spurt period 112. Yet, it uses Rate ½ (i.e. half of the resources) during a talk-spurt period 114. As the amount of transmission data is further reduced, the MS transmits the data packets at Rate ¼ (i.e. ¼ of the resources) during a talk-spurt period 116. During a silence period 118, the MS uses the minimum resources supporting the minimum rate, Rate ⅛.
As described above, the constantly allocated resources are not fully utilized during the periods 114, 116 and 118. The existence of the resulting extra resources implies inefficient uplink scheduling. Therefore, uplink resources are wasted during the talk-spurt periods as well as during the silence periods.
FIG. 2 illustrates a conventional uplink resource scheduling for rtPS.
Referring to FIG. 2, the status of an MS is divided into a talk-spurt period and a silence period on the time axis. The talk-spurt period is an on-period with transmission of data packets to be sent from the MS, while the silence period is an off-period without any transmission of data packet.
In rtPS, the MS requests uplink resource allocation to a base station (BS) in steps 212 to 236. The requested resources are decided based on the amount of packet data to be transmitted from the MS. The BS allocates the requested uplink resources to the MS. The MS then transmits the data packets using the allocated resources during periods 210, 220 and 230.
In the illustrated case of FIG. 2, there are three talk-spurt periods 210, 220 and 230 according to data rates. The MS transmits data at Rate 1 during the first talk-spurt period 210, at Rate ½ during the second talk-spurt period 220, and at Rate ¼ during the third talk-spurt period 230. Therefore, the MS uses different amounts of resources during the periods. The talk-spurt periods change from 210 to 230 due to the decrease of data rate.
More specifically, upon generation of data packets to be transmitted, the MS requests resource allocation in step 212. The BS then allocates maximum resources to support a maximum rate (e.g. Rate 1). The MS transmits the data packets at Rate 1 using the allocated resources. The transmission of data packets at Rate 1 is repeated during the talk-spurt period 210.
As the amount of transmission data is reduced, and thus the data rate needs to be changed, the MS requests resource allocation supporting the decreased data rate (e.g. Rate ½) in step 222. The MS then transmits the data packets using allocated resources. The transmission of data packets at Rate ½ is repeated during the talk-spurt period 220.
When the data rate is further decreased during the talk-spurt period 230, the MS requests allocation of resources supporting the further decreased data rate (e.g. Rate ¼) in step 232. The MS then transmits data packets at Rate ¼. The transmission of data packets at Rate ¼ is repeated during the talk-spurt period 230.
After completing the data packet transmission, the MS operates using the minimum resources (e.g. Rate ⅛) during a silence period 240.
As noted from the above description, rtPS requires periodic polling (i.e. uplink resource request, steps 212 to 218, steps 222 to 226, and steps 232 to 236). Even within a period requiring the same amount of resources 210, 220 or 230, periodic polling takes place (in steps 214 to 218, steps 224 and 226, or steps 234 and 236). The unnecessary polling leads to a waste of uplink resources.
Since both UGS and rtPS allocate uplink resources periodically according to scheduling type irrespective of the real-time status of the MS, uplink scheduling cannot be performed efficiently, reflecting the time-variant status of the MS.
Compared to UGS and real time Polling Service (rtPS), Extended-real time Polling Service (ertPS) allocates resources upon a MS request and enables transmission of data packets using the allocated resources without polling until the resources are changed. The MS expects to receive the same resources from the BS without any further polling in ertPS.
When a data rate decrease is required, the MS transmits data packets at the decreased data rate. Simultaneously, the MS notifies the BS of the change of resources due to the decrease of the data rate. Therefore, the BS can use the extra resources saved from the MS for other purposes.
The MS uses the Extended PiggyBack Request (PBR) field of a Grant Management subheader to notify the BS of the change of the data rate. The Grant Management subheader has the following configuration.
TABLE 1SizeSyntax(bits)NotesGrant Management Subheader {—— if (scheduling service type==UGS) {——  SI1—  PM1—  FLI1—  FL4—  Reserved9Shall beset tozero  } else if (scheduling service type==Extended rtPS) {——  Extended piggyback request11 —  FLI1—  FL4—  } else {——  Piggyback Request16 —  }——}——
In Table 1, one Most Significant Bit (MSB) of Extended PBR is used as an indicator indicating the change of data rate. If the MSB is set to 1, it implies that the data rate is changed. The remaining 10 Least Significant Bits (LSBs) of Extended PBR indicate the changed data rate. If the MSB is set to 0, it implies that the data rate is unchanged.
Alternatively, the MS can request allocation of a bandwidth corresponding to a requested data rate by the Bandwidth Request (BR) field of a BR and Uplink (UL) transmit power report header which is formatted as follows.
TABLE 2HT = 1EC = 0Type (3) =BR (11)(1)(1)0b011UL TX Power (8)CID MSB (8)CID LSB (8)HCS (8)
Referring to Table 2, one MSB of BR is used as an indicator indicating the change of data rate. If the MSB is set to 1, it implies that the data rate is changed. The 10 LSBs of BR indicate the changed data rate. If the MSB is set to 0, it implies that BR and UL transmit power report header is a typical header requesting a bandwidth for resource allocation.
FIG. 3 illustrates a conventional uplink scheduling for ertPS.
Referring to FIG. 3, the status of an MS is divided into a talk-spurt period and a silence period on the time axis. The talk-spurt period is an on-period with transmission of data packets to be sent from the MS, while the silence period is an off-period without any transmission of data packet.
When transitioning from the silence period to the talk-spurt period, the MS requests resource allocation to the BS by a BR header in step 310. Table 2 above showing the bandwidth request and uplink transmit power report header is an example of the BR header. The BR header carries bandwidth request information requesting allocation of the same resources without any further polling.
Upon receipt of the BR header, the BS allocates resources corresponding to a maximum data rate periodically to the MS during the talk-spurt period 312. The MS transmits data at the maximum data rate.
When the data rate is to be changed, the MS transmits data at the changed data rate during the next talk-spurt period. The changed data rate is lower than the previous data rate. In the illustrated case Rate 1 decreases to Rate ½. Meanwhile, the MS notifies the BS of the change of data rate by a Grant Management subheader. Then the MS transmits data at the changed data rate periodically during the talk-spurt period 314.
Upon receipt of the Grant Management subheader, the BS allocates as minimum resources as supporting Rate ½. The BS then allocates the extra resources saved from the MS for other purposes.
If the data rate is further to be decreased during data transmission at Rate ½, the MS transmits data at Rate ¼ during the next talk-spurt period 316. Meanwhile, the MS notifies the BS of the change of data rate by a Grant Management subheader. Then the MS transmits data at the changed data rate periodically during the talk-spurt period 316. The BS allocates as minimum resources as supporting Rate ¼.
If the data rate is further to be decreased during data transmission at Rate ¼, the MS changes the data rate to Rate ⅛ for the next talk-spurt period. Meanwhile, the MS notifies the BS of the change of data rate by a Grant Management subheader. The BS then allocates as minimum resources as supporting Rate ⅛.
As described above, when the data rate decreases, the MS transmits information about the changed data rate to the BS by the Grant Management subheader, and the BS allocates resources to the MS according to the changed data rate.
However, it may occur that the MS wants to increase the decreased data rate during the talk-spurt period. In order to transmit uplink data at the increased data rate, the MS needs as much as possible uplink resources. However, there is no specified method for notifying the BS of the intention of the MS regarding the increase of the data rate. Accordingly, there exists a need for a method of increasing a decreased data rate in an MS during a talk-spurt period.
Conventionally, the BS periodically allocates resources supporting the minimum data rate to the MS during the silence period, and the MS, when transitioning from the silence period to the talk-spurt period, requests a bandwidth using the minimum resources. During the silence period, hence, the BS periodically allocates the MS uplink resources supporting transmission of a 6-byte BR header or uplink resources supporting transmission of a BR subheader in the form of a piggy back request as illustrated in Table 1, that is, a 6-byte Generic Medium Access Control (MAC) header and a 2-byte Grant Management subheader. While these minimum resources are needed for the MS to request a bandwidth for transitioning from the silence period to the talk-spurt period, the periodic resource allocation may not be needed because the MS does not know when to transition to the talk-spurt period.